Acoustic apparatus



June 2, 1970 J. v. BOUYOUCOS ACOUSTIC APPARATUS 2 Sheets-sheet 2 FiledJan. 27, 1965 INVENTOR.

JOHN v. BOUYOUCOS Fig. 4

3,516,052 Patented June 2, 1970 3,516,052 ACOUSTIC APPARATUS John V.Bouyoucos, Rochester, N .Y., assignor to General Dynamics Corporation, acorporation of Delaware Filed Jan. 27, 1965, Ser. No. 428,398 Int. Cl.H04r 23/02; G01v 1/14 US. Cl. 34012 14 Claims ABSTRACT OF THE DISCLOSUREA hydroacoustic amplifier is described having a housing including a pathfor the flow of pressurized hydraulic fluid through a valving orifice. Alever valve has an end of one of its arms disposed to sweep across theorifice, thereby modulating the flow of hydraulic fluid. The valve isactuated by a hydraulic transformer including a cylinder ofelectrostrictive material disposed in a hydraulic fluid filledcylindrical cavity. A movable button is disposed between the cylindricalcavity and the opposite end of the valve from the orifice and isactuated in response to variations in pressure in the cavity to operatethe lever valve so that it sweeps across the valving orifice. Anelectric signal applied to the electrostrictive cylinder is translatedinto hydroacoustic energy which is coupled to a diaphragm for radiationoutwardly from the housing.

The present invention relates to acoustic apparatus, and moreparticularly to hydroacoustic amplifiers by which is meant apparatus ofthe type which is adapted to control the flow or the particle velocityof a hydraulic fluid under pressure at frequencies Within the acousticrange, which includes the sonic and ultrasonic range.

Hydroacoustic amplifiers are particularly useful for generating lowfrequency underwater sound, since they can handle high acoustic power ata relatively low frequency while remaining small in size and weight.Among such amplifiers is the hydroacoustic oscillator-amplifierdescribed in US. Pat. No. 3,105,460 issued on Oct. 1, 1963 to John V.Bouyoucos.

Underwater object detection or communication by acoustic means isparticularly diflicult to effectuate at long range because of suchbarriers as attenuation, ambient noise, reverberation, multipatheffects, and propagation velocity variations along the transmissionpath. Attempts in the past to improve acoustic detection orcommunication means have been to lower the frequency and to increase thesize and power of electroacoustic equipment and to provide more complexsignal waveforms and concomitant signal processing techniques. Largesize electromagnetic, magnetostrictive, or piezoelectric transducers andcomplex equipment for their control have become necessary. Aside frombeing more expensive, valuable shipboard space is needed for the complexequipment.

Accordingly, it is an object of the present invention to provide animproved hydroacoustic amplifier for the generation of high energyunderwater signals having complex waveforms which are suitable for usein underwater object detection and communication, the improvedhydroacoustic amplifier being small in size as compared to conventionalequipment for the purpose.

It is another object of the present invention to provide an improvedhydroacoustic amplifier which produces high energy underwater signalsunder control of low energy input signals, which underwater signals areadapted to be in synchronism and in direct phase relation with theircontrolling input signals.

It is yet another object of the present invention to provide an improvedhydroacoustic amplifier which may be controlled so that the amplifier isuseful in arrays thereof.

It is still another object of the present invention to provide animproved hydroacoustic amplifier which is particularly useful forunderwater detection and communication.

It is another object of the present invention to provide an improvedhydroacoustic amplifier capable of operating over a wide frequencyrange.

It is still another object of the present invention to provide animproved hydroacoustic amplifier capable of generating compressionalwave energy which can be frequency and amplitude modulated.

Briefly described, a hydroacoustic amplifier embodying the inventionutilizes an electrical control signal applied to a piezoelectric,electrostrictive or similar electromechanical member to produce fluidpressure variations of controlled frequency, amplitude, and phase in afluid filled cavity. The pressure variations in the cavity are thenfluid coupled through a hydraulic transformer to a valving member whichcontrols the modulation of an otherwise steady flow of a fluid mediumunder pressure through an acoustic chamber. Modulation, in accordancewith an embodiment of the invention, is effected by a valving structureincluding a mechanical transformer (e.g. a lever valve) which isoperated by the hydraulic transformer to obtain a large valve strokefrom a small movement of the electrical control signal responsivemember. Acoustic energy is generated in the chamber as a result of themodulation of the flow of fluid therethrough. The acoustic energy sogenerated may be coupled out to a load, such as the radiation load of alarge body of water, through a suitable coupling structure.

The invention itself both as to its organization and operation as wellas additional objects and advantages thereof will become more readilyapparent from a reading of the following description in connection withthe accompany drawings in which:

FIG. 1 is a rear elevation of hydroacoustic apparatus including ahydroacoustic amplifier embodying the present invention;

FIG. 2 is a cross sectional view of the apparatus of FIG. 1 taken alongline 22 of FIG. 1 when looking in the direction of the arrows;

FIG. 3 is an enlarged fragmentary view, in perspective, of a portion ofthe hydroacoustic amplifier of FIG. 1 showing a valving member and anoutlet stator port structure;

FIG. 4 is a sectional view of the hydroacoustic transducer of FIG. 1taken along line 4-4 of FIG. 1 when viewed in the direction of thearrows, the line 4-4 being perpendicular to the line 22;

FIG. 5 is a fragmentary perspective view of one bearing block whichsupports the valving member shown in FIGS. 3 and 6;

FIG. 6 is a sectional view of the hydroacoustic amplifier of FIG. 1taken along line 6-6, which is parallel to line 4-4, looking in thedirection of the arrows appended to the line 66, the view showing inmore detail the electrostrictive means also shown in FIG. 2; and

FIG. 7 is a schematic diagram of an electrical circuit employed in thehydroacoustic amplifier of FIG. 1.

Referring more particularly to FIGS. 1 and 2, there is shown ahydroacoustic amplifier 10. A valving housing 12 and a chamber housing13 of the amplifier are connected by bolts 14. An inlet connection 17 isprovided in the chamber housing 13 for receiving a low viscosityhydraulic fluid under pressure from an appropriate unidirectional flowsource or pump 20 through a main feed line 18. A suitable fluid ishydraulic oil S.A.E. 10. The hydraulic fluid is pumped into an acoustictank circuit 21 in the chamber housing 13. The acoustic tank circuitincludes an acoustic chamber 22 having a given acoustic stiffnessreactance and an inertance line 23 having a given acoustic inertivereactance which is substantially equal to the stiffness reactance of theacoustic chamber 22 at the mean operating frequency of the amplifier. Bymean operating frequency is meant the center frequency of the range offrequencies over which the amplifier is designed to operate. A receivingchamber 24 is provided between the acoustic tank circuit 21 and theinlet connection 17. The receiving chamber 24 serves to define apressure release termination or acoustic ground to the inertance line23. The acoustic tank circuit 21 is similar to the acoustic tank circuitdescribed in the above-referenced US. Pat. No. 3,105,460. The acousticchamber 22 includes an inlet at 25 and an outlet which is configured toprovide a stator port structure 26 for a valving member 31.

The hydraulic fluid enters the acoustic chamber 22 at inlet 25 andpasses through the chamber 22 and through the outlet stator portstructure 26 to an exhaust chamber 27 in the valve housing 12. Theexhaust chamber 27 includes an outlet connection 28 which is connectedto a main return line 29. The main return line 29 is connected to aninput connection 30 of the pump 20.

The valving member 31 is interposed between the outlet stator portstructure 26 and the exhaust chamber 27 and is operative to modulate theflow of fluid through the outlet stator port structure 26 in response toa motivating force, hereinafter to be defined. The valving member 31 ismounted on a shaft 32 which is supported on a pair of bearing supportblocks 33 and 34 (FIGS. 4 and The valving member 31 may be adjustable onthe shaft 32 and is clamped to the shaft 32 by locking screws 35. Theshaft 32 is pinned to the pair of bearing blocks 33 and 34 by pins 36and 46. The shaft 32 is made of an elastic material such as steel andhas reduced sections 37 and 38 which establish a torsion springsuspension for valve member 31. The effective rotary mass of valvemember 31 and the torsional spring rate of reduced sections 37 and 38define a natural or resonant frequency for the combination of thevalving member 31 and shaft 32 which resonant frequency is substantiallyequal to the mean operating frequency the amplifier 10.

The valving member 31 includes at one end 41 a cylindrically curvedvalving surface 39 which is contiguous to a corresponding cylindricallycurved valving surface 40 of the outlet stator port structure 26 (FIG.3). The valving member 31 also includes a metering edge 42 at its end41. The metering edge 42 traverses the stator port structure 26 anddefines the opening through which the fluid flows. The valving surfacesslide over each other, being separated by a lubricating film of thefluid. The metering edge thus has a wiping action.

The stator port structure 26 includes a rectangular opening 43 which hasa length which is just slightly less than the length of the meteringedge 42 of the valving member 31. The opening 43 has an edge or rim 48which, in conjunction with the metering edge 42, defines a variableorifice 49. The valving member 31 is rotatable about the longitudinalaxis of the shaft 32 as indicated by the arrows in FIG. 3, to vary thecross-sectional area of the orifice 49.

The valving member 31 includes a lever portion 44 opposite the end 41for rotating the valving member when the motivating force is appliedthereto. The lever portion 44 has at least two oppositely disposedbearing points 70 and 71 which bearing points 70 and 71 may be forexample less than one-quarter of the length of the valving member 31away from the axis of the shaft 32 so that movement magnification at theone end 41 may be achieved. As illustrated in FIG. 3 for example, thedistance of the bearing points 70 and 71 of the lever portion 44 fromthe axis of the shaft 32 is approximately one-quarter of the distance ofthe one end 41 of the valving member 31 from the axis of the shaft 32,so that a magnification factor of four is achieved.

Thus a small rotary movement of the lever portion 44 results in amagnified movement of the metering edge 42 of the valving member 31which in turn results in a relatively large change in the orifice areaof the orifice 49.

The assembly comprising the shaft 32, the valving member 31 and thesupporting blocks 33 and 34 desirably has suflicient stiffness andrigidity to support end thrusts arising from pressure variations in thechamber 22, without undergoing significant deflection or deformationrelative to the stator port structure 26.

Referring now to FIGS. 4 and 5 the bearing blocks 33 and 34 are boltedto the chamber housing as by bolts 45 which extend through the holes 45ain the blocks (FIG. 5). The bearing blocks 33 and 34 are of similarconstruction. Each of the bearing blocks may include a bearing 60 toreduce friction between the block 33 and shaft 32. The bearing blocks 33and 34 support the valving member 31 as was mentioned previously, sothat there is little or no end play of the valving member 31 relative tothe outlet stator port structure 26.

The valving member 31 is controllably rotated about the longitudinalaxis Of the shaft 32 by an electrostrictive excitation means 50. Theelectrostrictive excitation means 50 include first and secondelectrostrictive cylinders 51 and 52, for example of BaTiO coated withconductive material on their inner and outer cylindrical peripheralsurfaces, centrally disposed in first and second cavities 53 and 54respectively in the valving housing 12. The cavities 53 and 54 havecylindrical walls, FIG. 2 shows a cross-sectional view of the first andsecond electrostrictive cylinders 51 and 52 and the cavities 53 and 54.The electrostrictive cylinders 51 and 52 are electrically grounded tothe valving housing 12 by electrically conductive leaf springs 55, suchas Phosphor bronze springs, interposed between each of the cavities 53,54 and the outer peripheral surfaces of the electrostrictive cylinders51 and 52. As shown in FIGS. 2 and 6, the springs 55 may be spacedapproximately 120 apart near each of the ends 56 and 57 of theelectrostrictive cylinders 51 to insure a good electrical ground.

A portion of the electrostrictive means 50 is shown more in detail inFIG. 6. FIG. 6 shows in cross-sectional view the valve housing 12, thecavity .53 in the housing 12 and the electrostrictive cylinder 51disposed in the cavity 53. The cylinder 51 is interposed between tworesilient 0 rings 58 and 59 which provide a fluid seal at the ends 56and 57 of the electrostrictive cylinder 51, While allowing forlongitudinal and radial motion of the cylinder 51. The same type ofsealing rings 58 and 59 are provided for the other electrostrictivecylinder in the cavity 54.

Interposed between the cavities 53 and 54 and the valving member 31 arethe piston buttons 63 and 64 respectively which communicate themotivating force due to fluid pressure variations within the cavities 53and 54 to the lever portion 44 of the valving member 31.

The piston buttons 63 and 64 are slidably disposed and in a sealingrelationship within two cylindrical passages 8 and 9. The passages 8 and9 are coaxially aligned and have their longitudinal axis transverse tothe lever portion 44 the points and 71. The cylindrical passages 8 and 9communicate with the cavities 53 and 54 respectivley. The fluid pressurevariations in the cavity 53 are comcmunicated to the piston button 63 bya relatively small volume of captive fluid which is substantiallyconfined by the volume bounded by the outer surface of theelectrostrictive cylinder 51, the piston button 63 and the side wall andends of the cavity 53. In a like manner, the fluid pressure variationsin the cavity 54 are also communicated to the piston button 64 by arelatively small volume of captive fluid which is substantially boundedby the outer surface of the electrostrictive cylinder 52, the pistonbutton 64 and the side wall and ends of the cavity 54. The small volumeof the captive fluid in each of the cavities 53 and 54 is associatedwith a high acoustic stiflness so that the captive fluid behaves, by andlarge as an incompressible fluid. The piston buttons are free to movewith respect to the cavities 53 and 54 and present a relatively lowimpendance to AC fluid pressure variations so that substantially all ofthe AC volume displacement generated by the motion of theelectrostrictive cylinders provide equivalent displacement of the pistonbuttons.

The cavities 53 and 54 are connected to the high pressure side of thepump 20 at inlet 61 and 62 by way of inertance lines 90 and 91respectively. The pump 20 maintains a constant steady (DC) fluidpressure in the cavities 53 and 54 and provides a biasing force onpiston buttons 63 and 64 so that the pistons remain at all times incontact with the lever arm 44 at contact points 70 and 71. No fluidreturn is provided for the cavities 53 and 54 since the steady, DCpressure is maintained therein about which the AC fluid pressure, whichis produced in the amplifier, varies. The inertance lines 90 and 91 havea small cross sectional area and present a high impedance to AC pressurevariation generated in the cavities 53 and 54 and thus substantiallyprevent any AC volume current to be shunted away from the pistonbuttons.

The piston buttons 63 and 64 each have a relatively small area exposedto the captive fluid in each of the cavities '53 and 54 respectively ascompared to the area of each of the electrostrictive cylinders 51 and52. Small radial motions of the electrostrictive cylinders 51 and 52 ofopposite sense cause a relatively high linear displacement of the pistonbuttons 63 and 64 along the the longitudinal axis thereof. The ratio ofthe linear displacements of the piston buttons 63 and 64 to the linearradial displacements of the electrostrictive cylinders 51 and 52 willequal approximately the ratio of the effective driving areas of theelectrostrictive cylinders 51 and 52 to the driven area of the pistonbuttons '63 and 64. The combination of the electrostrictive cylinderswith its respective fluid cavity and piston button forms a hydraulictransformer to enable a small linear motion of the cylinder surface tobe transformed into a relatively larger motion of the piston button.This hydrualic transformer action coupled with the aforementioned rotarymechanical transformer action of the lever arm 44 and the valving arm 41as referenced to the axis of rotation of shaft 32 allows a small linearmotion of the surfaces of the electrostrictive cylinders 51 and 52 to betransformed into a large valving stroke of metering edge 42, and acorrespondingly large variation in the area of orifice 49.

The large valving stroke magnification resulting from the transformeractions provides for eflicient power conversion, and effective flowcontrol. Furthermore, the large valving stroke increases the powerhandling capacity of the amplifier.

The electrostrictive cylinders 53 and 54 are polarized so that anelectrical signal vlotage applied across inner electrodes 65 and 66 andouter electrodes 67 and 68, these electrodes being provided by thecoatings referred to above, of the electrostrictive cylinders 51 and 52respectively will cause the cylinders 51 and 52 to move radially in aphase opposed sense so that the valving member 31 may be alternatelyrocked about the shaft 32 to vary the area of the orifice 49 and tocontrol the flow of fluid from acoustic chamber 22 to the exhaustchamber 27.

FIG. 7 shows the electrical circuit 70 for the hydroacoustic amplifier10. The electrostrictive cylinders 51 and 52 are illustrated ascapacitors 51 and 52 since their electrical properties correspond tocapacitors. The capacitors or electrostrictive cylinders 51 and 52 aregrounded on one side which may be for example the valving housing 12 orby a lead wire 76 to ground by way of outer electrodes 67 and 68 on theelectrostrictive cylinders 51 and 52. The inner electrodes 65 and 66 ofthe capacitors or electrostrictive cylinders 51 and 52 are connected toinput terminals 73 and 74 respectively by lead wires 77 and 78. Theelectrical circuit 70 for illustrative purposes may be connected to aninput signal source not shown by way of a coupling transformer 75 sothat a signal applied to the coupling transformer 75 will give twoelectrical outputs which will be 180 out of phase with each other whenapplied to the capacitors or electrostrictive cylinders 51 and 52. Asignal applied to coupling transformer 75 will thus causeelectrostrictive cylinders 51 and 52, when polarized, to alternatelyexpand and contract to increase and decrease the pressure in thecavities 53 and 54 respectively. When a plurality of amplifiers areconnected in an array, say for underwater object detection orsignalling, the input signals may be applied simultaneously orselectively, by way of suitable switching, to the input transformers ofeach amplifier.

The lead wires 76, 77 and 78 may extend through an insulating boot and aslot 81 in the valving housing 12. FIG. 6 shows a watertight insulatedterminal '84 for lead wire 77. The terminal 84 is mounted in an end plug85 which is bolted to the valving housing 12 as by bolts 86. A similarend plug not shown is provided for the other electrostrictive cylinder52 and cavity 54.

A flexural disc radiating element 80 is shown in FIGS. 2 and 4, which isclamped to the chamber housing 13 by bolts 81. A piston 82 couplesacoustic energy from the acoustic chamber 22 to the flexural discradiating element 80. The acoustic signals produced by piston 82 aresimilar in waveform to the electrical input signals. Accordingly byapplying electrical input signals in controlled phase relation to aplurality of amplifiers in an array thereof, acoustic signals which aredirectional in nature can be produced. Also the acoustic signals canhave complex waveforms to represent information for signalling purposes.

In the operation of the hydroacoustic amplifier 10 the hydraulic fluidunder pressure is fed from the pump 20 through the main feeder line 18to the receiving chamber 24. The fluid is then fed through the inertanceline 23 and the acoustic chamber 22 all of which define the acoustictank circuit 21. In the unoperated condition the valving member 31 isnormally in a zero lap position such that metering rim 42 of valvingmember 31 is in line with metering rim 48 of stator port 26. In thisposition a small leakage flow passes from chamber 22 through theclearance gap between the end surface 39 of valving member 31 and endsurface 40 of stator port structure 26 to the exhaust chamber 27. Thefluid from the exhaust chamber 27 flows into the main return line 29through the outlet connection 28 to the input connection 30- of theconstant delivery pump 20. The pump 20 maintains a constant steady or DCfluid pressure in the cavities 53 and 54. Thus, in the unoperated orquiescent condition there may be a small, steady leakage flow of fluidunder pressure through the acoustic tank circuit 21, through the outletstator port structure 26, the exhaus chamber 27 and back 0 the pump 20.

If an electrical signal is now applied through the transformer 75 to theelectrostrictive cylinders 51 and 52, these cylinders will alternatelyexpand and contract out of phase with respect to each other. Theelectrostrictive cylinder 51 for example, may expand radially during apositive phase of the signal to cause a positive-going pressure withrespect to the average pressure in the fluid between the sidewall of thecavity 54 and the electrostrictive cylinder 52 so that the piston button64, in response to the increased pressure in the cavity 54, exerts apositive force acting in a clockwise direction on the lever portion 44of the valving member 31. During this same phase the otherelectrostrictive cylinder 51 may contract to cause a negative-goingpressure with respect to the average pressure in the fluid in the othercavity 53. This negative-going pressure exerts a negative force actingthrough piston button 63 in a clockwise direction on the lever portion44 of the valving member 31. In response to the net clockwise forceexerted on the portion 44, the valving member 31 rotates in a clockwisedirection to open the orifice 49 of the outlet stator port structure 26.

It can also be seen that the valving member 31 strokes to a closedposition for orifice 49 during a negative phase of the signal when theelectrostrictive cylinder 52 contracts and the electrostrictive cylinder51 expands.

The valving member 31 may open the orifice 49 for 50 percent of the timefor a given AC electrical signal voltage to give a single-ended class Bopertion at the given frequency. Class A, B, or C operation may beobtained by adjusting the position of the valving member 31 relative tothe outlet stator port structure 26 to allow the orifice 49 to be openfor various time periods during a given period of the electrical inputsignal. This adjustment can be accomplished by loosening the clampingscrews 35 and moving the valving member about the shaft 32.

The type or class of modulation in the hydroacoustic amplifier dependsupon the average position of the metering edge 42 with respect to therim 48 of the orifice 49. If the orifice 49 is open for substantiallymore than 50 percent of the period of the applied signal thehydroacoustic amplifier 10 operates in a single-ended class A manner. Ifthe orifice 49 is open for approximately 50 percent of the period asingle-ended class B operation is achieved. If the orifice 49 is openfor less than 50' percent of the period of the applied signal, asingle-ended class C operation is achieved. Furthermore, the outputfrequency of the amplifier 10 may be doubled by adjusting the travel ofthe valving member 31 to traverse the rectangular opening 43 twiceduring each cycle. 'In effect, the edge of the valving member oppositethe metering edge 42 may now also serve to define another orifice withthe outlet stator port structure 26.

For maximum power transfer, maximum efficiency, and minimum distortionin the output signal, the fundamental frequency of the modulated flowthrough orifice 49 at the mean frequency of amplifier operation shouldcorrespond simultaneously to the resonant frequency of the tank circuit21 and the resonant frequency of the coupling structure 80. Although theinstantaneous volume velocity through the orifice 49 for single-endedclass B or C operation, may not be sinusoidal for a sinusoidalexcitation signal voltage input, the acoustic filter action provided bythe resonant tank circuit 21 and coupling structure 80 can insure thatthe signal transferred to the load is a non-distorted replica of theexcitation signal voltage input.

Although two electrostrictive cylinders 51 and 52 have been shown,providing for a push-pull form of drive of the valving member 31, it isevident that one cylinder could be used to provide single-ended drivewith the static or average biasing force exerted by the correspondingone piston button on the lever arm 44 supported by an average torsionaldeflection of the torsionsprings 37 and 38 of shaft 32.

From the foregoing description, it will be apparent that there has beenprovided an improved hydroacoustic amplifier suitable for use inunderwater sound applications. Although one embodiment of thehydroacoustic amplifier has been described it will be appreciated thatvariations and modifications therein within the scope of the inventionwill undoubtedy become apparent to those skilled in the art.Accordingly, the foregoing description should be taken merely asillustrative and not in any limiting sense.

What is claimed is:

1. A hydroacoustic amplifier comprising (a) a chamber having an inletand an outlet port structure for the flow of a fluid medium underpressure therethrough,

(b) a valving member operatively mounted in cooperative relationshipwith said outlet port structure for modulating the flow of said fluidmedium output through said outlet port structure, and

(c) hydraulic transformer means coupled to said valving member andresponsive to an applied electrical input signal for operating saidvalving member to modulate the flow of said fluid medium through saidoutlet port structure to thereby derive acoustic energy in said chamber,said hydraulic transformer means including an electromechanicaltransducer having a first surface which changes dimensions as a functionof said signal, means coupled to said valving member having a secondsurface having an area different from the area of said first surface,said first and second surfaces being fluid coupled to each other.

2. The invention according to claim 1 further provided with meansconnected to said chamber for coupling said acoustic energy in saidchamber to a load.

3. The invention according to claim 1 wherein said electromechanicaltransducer includes an electrostrictive cylinder disposed in a fluidfilled cavity and wherein said means coupled to said valving memberincludes a movable piston button coupled to said cavity for transferringpressure variations in said cavity to said valving member.

4. The invention according to claim 3 wherein said electrostrictivecylinder has a greater surface area than the cross sectional area ofsaid piston button so that a small radial expansion of saidelectrostrictive cylinder in response to a signal voltage appliedthereto produces a high linear displacement of said piston button awayfrom said cavity.

5. In a hydroacoustic amplifier, the combination comprising (a) achamber having an outlet port structure and an inlet for the flow of afluid medium under pressure therethrough,

(b a valving mmeber operatively mounted in cooperative relationship withsaid outlet port structure for selectively modulating the flow of saidfluid medium through said chamber, and

(c) hydraulic means coupled to said valving member and responsive to anapplied electrical input signal of variable frequency and amplitude forcontrollably operating said valving member to selectively modulate theflow of said fluid medium through said outlet port structure to therebyderive in said chamber acoustic energy having a frequency and amplitudecorresponding to said variable frequency and amplitude.

6. The invention defined in claim 5 wherein said valving member isconnected in cooperative relationship with said hydraulic means tomodulate the flow of said fluid medium through said outlet portstructure at twice the frequency of said electrical input signal.

7. In a hydroacoustic vibration amplifier the combination comprising (a)a chamber having an inlet and an outlet port structure for the flow of afluid medium under pressure therethrough,

(b) first means including at least one valving member resilientlymounted in cooperative relationship with said outlet port structure formodulating the flow 'of said fluid medium through said chamber, and

(c) hydraulic means coupled to said valving member and responsive to anapplied electrical input signal having a frequency falling within agiven broad band of frequencies for selectively operating said valvingmember,

(d) said valving member having a resonant frequency falling within saidgiven broad band of frequencies.

8. A hydroacoustic amplifier comprising (a) an acoustic chamber havingan outlet port structure and an inlet for the flow of a fluid mediumunder pressure therethrough,

(b) a normally open valving member coupled to said outlet port structureto modulate said flow of said fluid medium through said acoustic chamberwhen operated,

(c) at least one cavity adapted to contain a fluid under pressure,

(d) coupling means communicating with said valving member and saidcavity for transmitting pressure variations in said one cavity tooperate said valve, and

(e) means including an electrically responsive device which changesdimensions in all directions in response to an electrical voltagepartially filling said one cavity to introduce pressure variations insaid one cavity to operate said valving member so that acoustic energyis generated in said acoustic chamher when said valving member isoperated.

9. In a hydroacoustic amplifier having a valving member for modulatingthe flow of a fluid medium under pressure for the generation of acousticenergy when said valving member is vibrated, apparatus for vibratingsaid valving member comprising:

(a) ahousing,

(b) at least one cavity disposed in said housing and adapted to containa fluid under Pressure therein,

(c) an electrically responsive device which changes dimensions inresponse to an electrical voltage applied thereto,

(d) said electrically responsive device partially filling said cavitywhereby pressure variations are introduced in said cavity when saidelectrical voltage is applied thereto, and

(e) means including a movable piston button communicating with saidcavity for vibrating said valving member in response to pressurevariations within said cavity.

10. The invention defined in claim 9 wherein said electricallyresponsive device is an electrostrictive element.

11. The invention defined in claim 9 wherein said electricallyresponsive device is an electrostrictive cylinder.

12. The invention defined in claim 9 further including means formaintaining a steady fluid pressure within said cavity about which saidpressure variations are introduced in said cavity by said electricallyresponsive device.

13. The invention defined in claim 9 wherein said electricallyresponsive device has a larger surface exposed in said cavity than saidmovable piston button.

14. In a hydroacoustic amplifier having a valving memher for modulatingthe flow of a fluid medium under pressure for the generation of acousticenergy when said valving member is vibrated, apparatus for vibratingsaid valving member comprising (a) ahousing,

(b) first and second cavities disposed in said housing and adapted tocontain a fluid under pressure therein,

(c) first and second electrostrictive elements partially filling saidfirst and second cavities respectively,

(d) means for applying an electrical signal in phase opposition to saidfirst and second electrostrictive elements to alternately inducepositive and negative going changes in dimensions in said first andsecond electrostrictive cylinder respectively, to induce correspondingfluid pressure variations in said first and second cavities, and

(e) means including first and second movable piston buttons exposed tosaid fluid in said first and second cavities respectively at one endthereof and coupled to said valving member at the other end thereof forcommunicating pressure variations in said first and second cavity tosaid valving member.

References Cited UNITED STATES PATENTS 2,161,980 6/1939 Runge et al3108.2 2,454,264 11/1948 Stigter 340-10 2,498,737 2/ 1950 Holden 310-9.62,991,594 7/1961 Brown et a1. 51--59 3,105,460 10/1963 Bouyoucos116--137 3,143,999 8/1964 Bouyoucos 116137 3,212,472 10/ 1965 Bouyoucos116-137 3,212,473 10/1965 Bouyoucos 116-137 3,267,421 8/1966 Robinson etal 3408 X 3,349,367 10/1967 Wisotsky 340 -8 X RODNEY D. BENNETT, JR.,Primary Examiner B. L. RIBANDO, Assistant Examiner US. Cl. X.R. 181.5

